Linear power amplifier arrangement and method for its operation

Abstract

A linear power amplifier arrangement is used for providing a selectable amount of amplification to a radio frequency signal to be amplified. The arrangement comprises a first parallel amplifier branch and a second parallel amplifier branch and means for conducting the radio frequency signal to be amplified selectably to one of the parallel amplifier branches. Additionally it comprises in the first parallel amplifier branch a series connection of a predistorter and a nonlinear amplifier, where said predistorter is arranged to compensate for the nonlinearity of said nonlinear amplifier.

What is claimed is:  
     
       1. A linear power amplifier arrangement for providing a selectable amount of amplification to a radio frequency signal to be amplified, comprising: 
       a first parallel amplifier branch and a second parallel amplifier branch,  
       means for conducting the radio frequency signal to be amplified selectably to one of the parallel amplifier branches, and  
       in the first parallel amplifier branch a series connection of a predistorter and a nonlinear amplifier,  
       wherein said predistorter is arranged to compensate for the nonlinearity of said nonlinear amplifier;  
       a first adjustable phase shifter in the first parallel amplifier branch;  
       a second adjustable phase shifter in the second parallel amplifier branch; and  
       a phase detector arranged to compare the phases of signals in the first and second parallel amplifier branches and to adjust at least one of said first and second adjustable phase shifters as a response to said comparison of phases.  
     
     
       2. The linear power amplifier arrangement of claim  1 , comprising in the second parallel amplifier branch a linear amplifier. 
     
     
       3. The linear power amplifier arrangement of claim  1 , comprising in the second parallel amplifier branch a series connection of a predistorter and a nonlinear amplifier. 
     
     
       4. The linear power amplifier arrangement of claim  1 , wherein 
       the linear power amplifier arrangement has a certain dynamic range of amplification extending from a low end to a high end,  
       the first parallel amplifier branch is dimensioned for maximal efficiency at the high end of the dynamic range, and  
       the second parallel amplifier branch is dimensioned for maximal efficiency at the low end of the dynamic range.  
     
     
       5. The linear power amplifier arrangement of claim  1 , comprising a nonzero integer number of parallel amplifier branches with a separate series connection of a predistorter and a nonlinear amplifier in each of them, and additionally comprising an integer number of parallel amplifier branches with a linear amplifier in each of them. 
     
     
       6. A radio communication device for processing and transmitting a radio frequency signal with a selectable transmission power, comprising: 
       a linear power amplifier arrangement for amplifying the radio frequency signal to a selected power level;  
       the linear power amplifier arrangement comprising:  
       a first parallel amplifier branch and a second parallel amplifier branch and selection means for conducting the radio frequency signal to be transmitted selectably to one of the parallel amplifier branches, and  
       in the first parallel amplifier branch a series connection of a predistorter and a nonlinear amplifier, where said predistorter is arranged to compensate for the nonlinearity of said nonlinear amplifier; and  
       a control block for controlling the operation of said selection means for selectively establishing the conduction of the radio frequency signal to be transmitted through either the first or the second parallel amplifier branch; and  
       means for operating as a terminal of a cellular radio system which comprises a number of base stations, so that said control block is arranged to process power control messages received from a base station and to establish the need for selecting a new parallel amplifier branch in the linear power amplifier arrangement on the basis of processed power control messages.  
     
     
       7. The radio communication device of claim  6 , additionally comprising means for operating as a terminal of a cellular radio system employing continuous phase modulation, whereby the radio communication device further comprises, in association with the linear power amplifier arrangement, a first adjustable phase shifter in the first parallel amplifier branch, a second adjustable phase shifter in the second parallel amplifier branch and a phase detector arranged to compare phases of signals in the first and second parallel amplifier branches and to adjust at least one of said first and second adjustable phase shifters as a response to said comparison of phases. 
     
     
       8. A method for adjusting an output power of a linear power amplifier arrangement comprising a first parallel amplifier branch and a second parallel amplifier branch, the method comprising the steps of 
       selecting the first parallel amplifier branch for operation; and  
       in the first parallel amplifier branch, nonlinearly predistorting a signal to be amplified and subsequently nonlinearly amplifying it so that the nonlinearities of the predistortion and amplification substantially cancel each other; and  
       before selecting the first parallel amplifier branch for operation, having the second parallel amplifier branch selected for operation;  
       enabling a conduction of the signal to be amplified to both the first parallel amplifier branch and the second parallel amplifier branch;  
       measuring a phase difference between a signal in the first parallel amplifier branch and a signal in the second parallel amplifier branch;  
       shifting a phase of the signal in the first parallel amplifier branch to make it coincident with a phase of the signal in the second parallel amplifier branch;  
       conducting the signal amplified in the first parallel amplifier branch out of the linear power amplifier arrangement as its output signal; and  
       disabling the conduction of the signal to be amplified to the second parallel amplifier branch.  
     
     
       9. The method of claim  8  further comprising the steps of: 
       in association with enabling the conduction of the signal to be amplified to both the first parallel amplifier branch and the second parallel amplifier branch, increasing a gain factor of the second parallel amplifier branch; and  
       in association with disabling the conduction of the signal to be amplified to the second parallel amplifier branch, decreasing a gain factor of the first parallel amplifier branch.